Field of the Invention
The present invention relates to a measuring system and a measuring instrument for measuring a physical quantity or a change in a physical quantity, in which the evaluation of a measuring signal is resolved in a spread manner or output on a dial in a variably scaled manner, depending on the measured value range traversed.
Description of the Background Art
In electrical switchgear, in particular, it is common practice to monitor the pressure or the density of an insulating gas. For example, SF6, sulfur hexafluoride, is a gas of this type for “gas-insulated switchgear” (GIS) of this type.
This gas is used as an insulating gas in electrical high-voltage switchgear for the purpose of facilitating higher performances than when using ambient air, since the insulation resistance of ambient air is limited at high voltages, which means that much greater distances must be maintained.
For this purpose, SF6 is held, for example, under a pressure of 1.2 to 2 bar. Certain machines are held between 0.4 and 0.6 or 0.8 MPa at a temperature of 20° C.
Depending on the temperature, this value is to be differently controlled due to the volume expansion of the gas, for which reason it has also been established to monitor the pressure in a temperature-compensated manner and thereby to obtain a signal proportionate to the density.
The pressure or the gas density is usually monitored in a gas-insulated switchgear for the purpose of monitoring the operation within a certain pressure or density range. For this purpose, it is advantageous to set one or multiple control points or switches in such a way that a warning or an alarm is output upon undershooting. At the same time, another control point or switch is set in such a way that an impermissible overpressure is also reported. However, since the working range, in particular the optimum pressure range for a switchgear, is very narrow, it is often difficult, in particular in conventional manometers, to reliably and precisely position multiple switches close together.